1. Field of the Invention
The present invention relates to a honeycomb structured body and an exhaust gas converting apparatus.
2. Discussion of the Background
Conventionally, honeycomb catalysts generally used for converting automobile exhaust gas are manufactured by supporting materials having high specific surface area such as activated alumina and catalyst metals such as platinum on the surface of a cordierite-based honeycomb structured body having an integral structure and low thermal expansive characteristics. Additionally, for the purpose of NOx treatment under excess oxygen atmosphere such as lean burn engine and diesel engine, alkaline earth metals such as Ba are supported as NOx-storage agents.
Meanwhile, in order to improve the converting performance, it is necessary to raise the contact probability between exhaust gas and the catalyst noble metals and NOx-storage agents. For that purpose, it is necessary to increase the specific surface area of the support and decrease the size of the noble metal particles and highly disperse them. Therefore, there are suggested honeycomb structured bodies in which the cell shape, cell density, wall thickness, and the like have been contrived (see, for example, JP-A 10-263416).
On the other hand, as the honeycomb structured body comprising high specific surface area materials, there have been known a honeycomb structured body obtainable by extrusion molding of inorganic fibers and inorganic binders (see, for example, JP-A 05-213681). Moreover, for the purpose of enlarging the size of such honeycomb structured body, there has been known one in which honeycomb units are bound one another through adhesive layers, and honeycomb units having the cross-sectional shape of 200 cm2 or more have been indicated (see, for example, DE 4341159).
To deal with this problem, there has been disclosed a honeycomb structured body with the cross-sectional shape thereof changed from an exactly circular shape to a flat shape to adjust the circularity for improving the holding force of the honeycomb structured body (see, for example, JP-A 2003-262118). Further, there has also been disclosed a honeycomb structured body having irregularities formed on the periphery thereof so as to adjust the circularity (see, for example, JP-A 2001-329836).
Other than the above-mentioned-honeycomb structured bodies, there has been disclosed a honeycomb structured body, in which a bonding layer provided in the diagonal portion of cells is set thick so as to increase the isostatic strength (see, for example, JP-A 2003-260322).
The contents of JP-A 10-263416, JP-A 5-213681, DE 4341159, JP-A 2003-262118, JP-A 2001-329836, and JP-A 2003-260322 are incorporated herein by reference in their entirety.